Thermally conductive sheet and method of manufacturing semiconductor device

ABSTRACT

A method of manufacturing a semiconductor device includes adhering together a heat dissipating body and a plurality of heat generating bodies via a thermally conductive sheet, by applying pressure to the heat dissipating body and the plurality of heat generating bodies in a thickness direction of the thermally conductive sheet with the thermally conductive sheet disposed therebetween, the thermally conductive sheet having a compression modulus of 1.40 MPa or less under a compressive stress of 0.10 MPa at 150° C.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S. Ser. No. 17/269,524, filed on Feb. 18, 2021, which is a national stage application of International Application No. PCT/JP2018/031196, filed on Aug. 23, 2018. Each of the above applications is hereby incorporated by reference, in its entirety, into the present application.

TECHNICAL FIELD

The present disclosure relates to a thermally conductive sheet and a method of manufacturing a semiconductor device.

BACKGROUND ART

In conjunction with the recent increasing wiring density of multilayer wiring boards, increasing wiring density in semiconductor packages, increasing mounting density of electronic components, and increasing heat generation per unit area due to the increased integration of semiconductor devices and the like, improved heat dissipation properties are desired for semiconductor devices.

Good heat dissipation properties are particularly required for semiconductor devices that generate large amount of heat, such as central processing units (CPUs) and power devices. These semiconductor devices have a configuration in which a heat generating body and a heat dissipating body made of aluminum, copper or the like are tightly adhered with a thermally conductive material, such as grease or a thermally conductive sheet, being disposed therebetween to allow heat dissipation (for example, see Patent Documents 1 to 4).

RELATED ART DOCUMENTS Patent Documents

[Patent Document 1] Japanese Patent Application Laid-Open (JP-A) No. H05-247268

[Patent Document 2] JP-A No. H10-298433

[Patent Document 3] Japanese Patent No. 4743344

[Patent Document 4] Japanese Patent No. 5316254

SUMMARY OF INVENTION Technical Problem

In conjunction with the recent improved performances of semiconductor packages, semiconductor chips and semiconductor packages have increased in size. In a case in which grease is used as a thermally conductive material, the size increase causes the occurrence of pump-out during thermal cycling, making it difficult to ensure sufficient heat dissipation.

Further, demand has recently been increasing for semiconductor devices configured by mounting plural heat generating bodies, such as integrated circuits such as CPUs and a graphic processing units (GPUs), and memories such as high bandwidth memories (HBMs), on a substrate. In a case in which grease is used as a thermally conductive material between a heat dissipating body and plural heat generating bodies, complicated processes are required since the grease needs to be applied to the respective heat generating bodies to adhere the heat generating bodies to the heat dissipating body. Further, in a case in which the respective heat generating bodies have different heights, grease cannot adjust to the height difference, which makes it difficult to sufficiently adhere the plural heat generating bodies and the heat dissipating body with each other. Even in a case in which a thermally conductive sheet is used as a thermally conductive material, there are cases in which conventional manufacturing methods fail to achieve sufficient heat dissipation by the thermally conductive sheet failing to adjust to the height difference of plural heat generating bodies.

In view of these circumstances, the present disclosure is directed to providing a method of manufacturing a semiconductor device that can produce a semiconductor device having an excellent heat dissipation property and that involves simple processes, and a thermally conductive sheet usable in producing a semiconductor device having an excellent heat dissipation property.

Solution to Problem Means for Solving the Above-Described Problems Include the Following Embodiments

-   -   (1) A method of manufacturing a semiconductor device, the method         including adhering together a heat dissipating body and a         plurality of heat generating bodies via a thermally conductive         sheet, by applying pressure to the heat dissipating body and the         plurality of heat generating bodies in a thickness direction of         the thermally conductive sheet with the thermally conductive         sheet disposed therebetween, the thermally conductive sheet         having a compression modulus of 1.40 MPa or less under a         compressive stress of 0.10 MPa at 150° C.     -   (2) The method of manufacturing a semiconductor device according         to (1), wherein the thermally conductive sheet has a thermal         conductivity of 7 W/(mK) or higher, the thermal conductivity         being obtained using a thermal resistance measured by a steady         state method.     -   (3) The method of manufacturing a semiconductor device according         to (1) or (2), wherein the thermally conductive sheet has a tack         strength of 5.0 N·mm or more at 25° C.     -   (4) The method of manufacturing a semiconductor device according         to any one of (1) to (3), wherein the pressure is from 0.05 to         10.00 MPa.     -   (5) The method of manufacturing a semiconductor device according         to (4), wherein the pressure is from 0.10 to 0.50 MPa.     -   (6) The method of manufacturing a semiconductor device according         to any one of (1) to (5), wherein the plurality of heat         generating bodies include a plurality of different kinds of heat         generating bodies.     -   (7) The method of manufacturing a semiconductor device according         to any one of (1) to (6), wherein an area of a face, of at least         one of the plurality of heat generating bodies, that faces the         thermally conductive sheet is 100 mm² or more.     -   (8) The method of manufacturing a semiconductor device according         to any one of (1) to (7), wherein the plurality of heat         generating bodies are provided on a substrate, and wherein an         area of a face of the substrate that faces the plurality of heat         generating bodies is 1000 mm² or more.     -   (9) The method of manufacturing a semiconductor device according         to any one of (1) to (8), wherein the plurality of heat         generating bodies include three or more heat generating bodies.     -   (10) A thermally conductive sheet having a compression modulus         of 1.40 MPa or less under a compressive stress of 0.10 MPa at         150° C., the thermally conductive sheet being for use in         adhering together a heat dissipating body and a plurality of         heat generating bodies of a semiconductor device, by disposing         the thermally conductive sheet between the heat dissipating body         and the plurality of heat generating bodies.     -   (11) The thermally conductive sheet according to (10), wherein         the thermally conductive sheet has a thermal conductivity of 7         W/(mK) or higher, the thermal conductivity being obtained using         a thermal resistance measured by a steady state method.

Advantageous Effects of Invention

According to the present disclosure, a method of manufacturing a semiconductor device that can produce a semiconductor device having an excellent heat dissipation property and that involves simple processes, and a thermally conductive sheet usable in producing a semiconductor device having an excellent heat dissipation property are provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view of a semiconductor device according to an embodiment of the present disclosure.

FIG. 2 is a diagram illustrating the amount of warpage of a heat generating body.

FIG. 3 is a plan view illustrating the positions of semiconductor chips on a substrate described in the Examples section.

DESCRIPTION OF EMBODIMENTS

Embodiments for carrying out the invention will be described below in detail. However, the invention is not limited to the following embodiments. In the following embodiments, components (including elemental steps, etc.) thereof are not essential unless otherwise specified. The same applies to numerical values and ranges, which do not limit the invention.

In the present disclosure, the term “step” encompasses an independent step separated from other steps as well as a step that is not clearly separated from other steps, as long as a purpose of the step can be achieved.

In the present disclosure, a numerical range specified using “(from) . . . to . . . ” represents a range including the numerical values noted before and after “to” as a minimum value and a maximum value, respectively.

In the numerical ranges described in a stepwise manner in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of another numerical range described in a stepwise manner. Further, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value of the numerical ranges may be replaced with the values shown in the Examples.

In the present disclosure, each component may include plural substances corresponding to the component. In a case in which plural substances corresponding to respective components are present in a composition, an amount or content of each component in the composition means the total amount or content of the plural substances present in the composition unless otherwise specified.

In the present disclosure, each component may include plural kinds of particles corresponding to the component. In the case in which plural kinds of particles corresponding to respective components are present in a composition, a particle diameter of the component means a value with respect to the mixture of the plural kinds of particles present in the composition, unless otherwise specified.

The term “layer” as used herein encompasses, when a region in which the layer or the film is present is observed, not only a case in which the layer is formed over the entire observed region, but also a case in which the layer is formed at only a part of the observed region.

The term “layered” as used herein means disposing layers on one another, in which two or more layers may be bonded with each other, or may be attachable to/detachable from one another.

In a case in which an embodiment is described herein with reference to a drawing, the configuration of the embodiment is not limited by the configuration illustrated in the drawing. The sizes of members in respective drawings are conceptual, and the relative relationships between the sizes of the members are not limited thereto.

<<Method of Manufacturing Semiconductor Device>>

A method of manufacturing a semiconductor device according to the present disclosure includes adhering together a heat dissipating body and a plurality of heat generating bodies via a thermally conductive sheet, by applying pressure to the heat dissipating body and the plurality of heat generating bodies in a thickness direction of the thermally conductive sheet with the thermally conductive sheet disposed therebetween, the thermally conductive sheet having a compression modulus of 1.40 MPa or less under a compressive stress of 0.10 MPa at 150° C. The method of manufacturing a semiconductor device according to the present disclosure can simplify the processes since it enables adhesion of a plurality of heat generating bodies to a heat dissipating body at a time.

[Heat Generating Body]

The heat generating body in the present disclosure is an object from which heat is released by adhering thereto a heat dissipating body via a thermally conductive sheet. Examples of the heat generating body include a semiconductor chip and a semiconductor package.

The size of the heat generating body is not particularly limited. For example, the area of the face of the heat generating body that faces the thermally conductive sheet may be 100 mm² or more, 200 mm² or more, or 400 mm² or more. The area of the face of the heat generating body that faces the thermally conductive sheet may be 10,000 mm² or less, 3000 mm² or less, or 1500 mm² or less.

The number of the heat generating bodies provided in a semiconductor device may be 2 or more, 4 or more, or 5 or more. The upper limit thereof is not particularly limited, and the number of the heat generating bodies may be 10 or less. A plurality of one type of heat generating bodies may be provided in one semiconductor device, or a plurality of different types of heat generating bodies (e.g., plural heat generating bodies having different lengths in the thickness direction of the thermally conductive sheet) may be provided in one semiconductor device. In particular, in a case in which plural different types of heat generating bodies are provided in one semiconductor device, the heat generating bodies tend to have different heights. However, the method of manufacturing a semiconductor device according to the present disclosure tends to achieve favorable heat dissipation by the thermally conductive sheet adjusting to the height difference.

[Heat Dissipating Body]

The heat dissipating body in the present disclosure is a member that dissipates heat from a heat generating body via a thermally conductive sheet. Examples of the heat dissipating body include a heat spreader, a heat sink, and a water cooling pipe.

[Substrate]

The plurality of heat generating bodies may be provided at a substrate. The substrate is not particularly limited, and examples thereof includes: an interposer substrate such as an organic substrate, an organic film, a ceramic substrate, or a glass substrate; a glass substrate for liquid crystal devices; a substrate for multi-chip modules (MCMs); or a substrate for hybrid ICs.

The size of the substrate is not particularly limited. For example, the area of a face of the substrate at which the plurality of heat generating bodies are provided may be 1000 mm² or more, 2000 mm² or more, 3000 mm² or more or 5000 mm² or more. The area of a face of the substrate at which the plurality of heat generating bodies are provided may be 10,000 mm² or less.

[Thermally Conductive Sheet]

The thermally conductive sheet used in the present disclosure has a compression modulus of 1.40 MPa or less under a compressive stress of 0.10 MPa at 150° C. In the present disclosure, the thermally conductive sheet is a sheet for use in adhering together a heat dissipating body and a plurality of heat generating bodies of a semiconductor device by being disposed between the heat dissipating body and the plurality of heat generating bodies. A sheet herein means a product in a sheet shape, which is not liquid, and is distinguished from grease, which is liquid. Here, “liquid” indicates a material having a viscosity of 1000 Pa·s or less at 25° C. The viscosity is defined as a value measured by a rheometer at a shear rate of 5.0 s⁻¹ at 25° C. The “viscosity” is measured at a temperature of 25° C. as a shear viscosity using a rotational shear viscometer equipped with a cone plate (diameter: 40 mm, cone angle: 0°).

In a case in which grease is used as a thermally conductive material between a heat generating body and a heat dissipating body, thermal resistance may increase owing to pump-out during the thermal cycling. However, the manufacturing method in the present disclosure does not experience the pump-out since a thermally conductive sheet is used.

Further, since the manufacturing method according to the present disclosure employs a thermally conductive sheet having the above-described compression modulus, even in a case in which the plurality of heat generating bodies have different heights, the thermally conductive sheet tends to be able to adjust to the height difference by being compressed by the application of pressure (pressing), whereby heat dissipation tends to be ensured.

The thermally conductive sheet used in the present disclosure is used for adhering a heat dissipating body and a plurality of heat generating bodies by being disposed between the heat dissipating body and the plurality of heat generating bodies. The thermally conductive sheet may be, for example, a thermal interface material 1 (TIM1) to be disposed between a semiconductor chip and a heat spreader, which are a heat generating body and a heat dissipating body, respectively. While grease has been conventionally used for TIM1, the thermally conductive sheet used herein is particularly useful in view of the fact that, in conjunction with the increase in size of the heat generating bodies, it has become difficult to ensure sufficient heat dissipation with grease.

The thermally conductive sheet has a compression modulus of 1.40 MPa or less, preferably 1.30 MPa or less, and more preferably 1.20 MPa or less, under a compressive stress of 0.10 MPa at 150° C. By the compression modulus being 1.20 MPa or less, the thermally conductive sheet can more easily adjust to the height difference of the plurality of heat generating bodies. The lower limit of the compression modulus under a compressive stress of 0.10 MPa at 150° C. is not particularly limited. The compression modulus may be 0.50 MPa or more, or 0.70 MPa or more.

The compression modulus of the thermally conductive sheet can be measured using a compression tester (e.g., INSTRON 5948 MICROTESTER, Instron Corporation). A load is applied to the thermally conductive sheet in the thickness direction at a displacement rate of 0.1 mm/min, during which the displacement (mm) and the load (N) are measured. The strain (dimensionless), which is determined as “displacement (mm)/thickness (mm)”, and the stress (MPa), which is determined as “load (N)/area (mm²)”, are plotted as the abscissa and the ordinate, respectively, and the slope at a certain stress is defined as the compression modulus (MPa). Specifically, the compression modulus can be measured by, for example, the method described in the Examples section.

The thermally conductive sheet preferably has tackiness from the viewpoint of improving adhesion. The thermally conductive sheet preferably has a tack strength at 25° C. of 5.0 N·mm or more, more preferably 6.0 N·mm or more, and further preferably 7.0 N·mm or more. By the tack strength being 5.0 N·mm or more, detachment of the thermally conductive sheet tends to be suppressed even when the respective heat generating bodies warp, thereby further improving heat dissipation. The upper limit of the tack strength is not particularly limited. The tack strength may be 20.0 N·mm or less, or 15.0 N·mm or less.

The tack strength of the thermally conductive sheet at 25° C. can be measured using a universal physical property tester (e.g., TEXTURE ANALYZER, Eko Instruments Co., Ltd.). A probe having a diameter of 7 mm is pressed against the thermally conductive sheet at a load of 40 N at 25° C. (ambient temperature) and is maintained for 10 seconds, and thereafter is lifted. The tack strength (N·mm) at 25° C. is obtained as an area determined by integrating the load-displacement curve resulting therefrom. Specifically, the tack strength can be measured, for example, by the method described in the Examples section.

The method of obtaining a thermally conductive sheet that has an compression modulus of 1.40 MPa or less under a compressive stress of 0.10 MPa at 150° C. is not particularly limited. For example, such a thermally conductive sheet can be obtained by adjusting the types and the blending ratio of the components used in the thermally conductive sheet, such as a thermally conductive filler and a resin.

The thermal conductivity of the thermally conductive sheet is not particularly limited, and higher thermal conductivity is preferable. The thermally conductive sheet preferably has a thermal conductivity of 7 W/(mK) or higher, more preferably from 10 W/(mK) or higher, and further preferably from 15 W/(mK) or higher, the thermal conductivity being obtained using a thermal resistance measured by a steady state method. By the thermal conductivity being 7 W/(mK) or higher, increase in thermal resistance tends to be suppressed even if the thermally conductive sheet is thickened in order to improve adjustability to warpage of heat generating bodies.

In the present disclosure, the thermal conductivity of the thermally conductive sheet is specifically determined as follows.

A thermally conductive sheet is cut into a 10 mm×10 mm piece, which is then disposed between a transistor (2SC2233) and a copper block, which are a heat generating body and a heat dissipating body, respectively. A current is applied to the transistor while the transistor is pressed at a pressure of 0.14 MPa at 80° C., at which time the temperature of the transistor T1 (° C.) and the temperature of the copper block T2 (° C.) are measured. A thermal resistance value X per unit area of 1 cm² (K·cm²/W) is calculated based on the measured values and the applied electric power W1 (W) as follows.

X=(T1−T2)×1/W1

Further, the thermal conductivity λ (W/(mK)) is calculated using the thickness t (μm) as follows.

λ=(t×10⁻⁶)/(X×10⁻⁴)

The thickness of the thermally conductive sheet is not particularly limited, and may be determined as appropriate in accordance with, for example, specifications of the semiconductor package or the like for which the thermally conductive sheet is to be used. The smaller the thickness is, the lower the thermal resistance tends to be, while the greater the thickness is, the more the adjustability to warpage tends to improve. The thermally conductive sheet may have an average thickness of from 50 to 3,000 μm and, from the viewpoints of thermal conductivity and adhesion, the thermally conductive sheet preferably has an average thickness of from 100 to 500 μm, and more preferably from 150 to 300 μm. The average thickness of the thermally conductive sheet can be determined by measuring the thickness at three spots using a micrometer and taking the arithmetic mean of the measured values.

The amount of compression of the thermally conductive sheet is not particularly limited. For example, the amount of compression under a compressive stress of 0.10 MPa at 150° C. may be from 20 to 1000 μm, from 30 to 200 μm or from 40 to 100 μm. These values may also be applied to the amount of compression under a compressive stress of 0.15 MPa at 150° C.

The “amount of compression” of a thermally conductive sheet refers to an amount of compression of the thermally conductive sheet that is being pressed in the thickness direction thereof, and is a value obtained by subtracting the thickness of the thermally conductive sheet that is being pressed from the thickness of the thermally conductive sheet before being pressed.

The compression ratio of the thermally conductive sheet is not particularly limited. For example, the compression ratio under a compressive stress of 0.10 MPa at 150° C. may be from 10 to 60%, from 15 to 50%, or from 15 to 40%. These values may also be applied to the compression ratio under a compressive stress of 0.15 MPa at 150° C.

The “compression ratio” of a thermally conductive sheet is a ratio (%) of the amount of compression (μm) with respect to the thickness (μm) of the thermally conductive sheet before being pressed.

A thermally conductive sheet provided with a protective film for protecting its adhesive surface on at least one side of the thermally conductive sheet may be prepared and used. In this case, a thermally conductive sheet, from which the protective film has been peeled off, is used for adhering together the heat generating bodies and the heat dissipating body. Examples of the protective film include: a resin film of polyethylene, polyester, polypropylene, polyethylene terephthalate, polyimide, polyether imide, polyether naphthalate or methyl pentene, polytetrafluoroethylene, ethylene tetrafluoroethylene copolymer, or perfluoroalkoxyalkane; a coated paper; a coated fabric; and a metallic foil of aluminum. One kind of protective film may be used singly, or two or more kinds thereof may be used in combination to form a multilayered film. It is preferable that the protective film is surface-treated with a releasing agent or the like, such as a silicone-based releasing agent or a silica-based releasing agent.

The thermally conductive film may have any composition as long as it satisfies the above-described specific compression modulus. Examples include a thermally conductive sheet containing a resin and a thermally conductive filler.

Examples of the thermally conductive filler include aluminum nitride, aluminum oxide, boron nitride, titanium oxide, zinc oxide, silicon carbide, silicon, silicon oxide, silica, glass, metal particles, carbon fibers, graphite, graphene, and carbon nanotubes. The thermally conductive filler may be surface-treated. One kind of thermally conductive filler may be used singly, or two or more kinds thereof may be used in combination.

The shape of the thermally conductive filler is not particularly limited, and may be spherical, ellipsoidal, flaky, granular, cylindrical, acicular or fibrous.

The average particle diameter of the thermally conductive filler is not particularly limited, and is preferably determined in accordance with the material of the thermally conductive filler or the like.

The aspect ratio (major axis/minor axis) of the thermally conductive filler is not particularly limited, and may be within the range of from 1 to 100, from 5 to 50, or from 10 to 40. The aspect ratio of the thermally conductive filler refers to an arithmetic mean value of measurement values obtained by measuring the ratio of the major axis with respect to the minor axis in 20 representative particles using a scanning electron microscope (SEM).

From the viewpoint of thermal conductivity, the thermally conductive filler is preferably oriented in the thickness direction of the thermally conductive sheet. The expression “oriented in the thickness direction” herein means that, in a thermally conductive filler having a major axis and a minor axis (i.e., having an aspect ratio exceeding 1), the angle between the major axis of the thermally conductive filler and the surface (i.e., main face) of the thermally conductive sheet (also referred to as “angle of orientation”) is 60° or more. The angle of orientation is preferably 80° or more, more preferably 85° or more, and further preferably 88° or more.

The content of the thermally conductive filler in the thermally conductive sheet is preferably determined in view of the balance between thermal conductivity and adhesiveness and the like, in accordance with the material or the like of the thermally conductive filler. For example, the content of the thermally conductive filler may be from 25 to 75% by volume, from 30 to 60% by volume, or from 35 to 50% by volume, with respect to the total volume of the thermally conductive sheet.

The resin contained in the thermally conductive sheet is not particularly limited, and may be, for example, a thermosetting resin or a non-thermosetting resin. Examples of the resin include an epoxy resin, silicone, an acrylic resin, a polyimide resin, a bismaleimide resin, a benzocyclobutene resin, a phenol resin, an unsaturated polyester, a diallyl phthalate resin, polyurethane, polyimide silicone, a thermosetting polyphenylene ether, a thermosetting modified polyphenylene ether, polybutene, polyisoprene, polysulfide, an acrylonitrile rubber, a silicone rubber, a carbohydrate resin, a terpene resin, a terpene phenolic resin, and a hydrogenated terpene phenol. One kind of resin may be used singly, or two or more kinds thereof may be used in combination.

The amount of the resin in the thermally conductive sheet is preferably determined in accordance with, for example, the type of resin or desired flexibility, tackiness, adhesiveness, sheet strength or resistance to hydrolysis. For example, the content of the resin is preferably from 25 to 75% by volume, more preferably from 40 to 70% by volume, and further preferably from 50 to 65% by volume, with respect to the total volume of the thermally conductive sheet.

The thermally conductive sheet may include an additive of a different kind in addition to the thermally conductive filler and the resin, such as a flame retardant or an antioxidant. The flame retardant is not particularly limited and may be selected from commonly used flame retardants as appropriate. Examples thereof include a red phosphorus flame retardant and a phosphate flame retardant. In particular, a phosphate flame retardant is preferable from the viewpoints of excellent safety and improved adhesiveness due to its plasticization effect.

The method of manufacturing the thermally conductive sheet is not particularly limited as long as a thermally conductive sheet having the above-described specific compression modulus and tack strength can be obtained. For example, the sheet may be produced by preparing a composition containing respective components of the thermally conductive sheet, and forming a sheet by rolling, pressing, extruding, coating or the like.

Further, the sheet may be produced by forming a shaped body using a composition containing respective components of the thermally conductive sheet, and slicing the shaped body. In this case, it is preferable that the shaped body is sliced such that the thermally conductive filler becomes oriented in the thickness direction.

In an embodiment, the thermally conductive sheet may be produced by preparing a composition containing respective components of the thermally conductive sheet, forming the composition in a sheet shape to obtain a sheet, forming a layered body by layering respective sheets on one another, and slicing a side face of the layered body. By producing a thermally conductive sheet using this method, efficient thermal conduction paths tend to be formed, and a thermally conductive sheet having a high thermal conductivity and excellent adhesiveness tends to be obtained. The obtained thermally conductive sheet may further be pasted to and laminated with a protection film.

[Method of Adhering Heat Generating Bodies and Heat Dissipating Body]

The method of manufacturing a semiconductor device in the present disclosure includes adhering together a heat dissipating body and a plurality of heat generating bodies via a thermally conductive sheet by applying pressure to the heat dissipating body and the plurality of heat generating bodies in a thickness direction of the thermally conductive sheet with the thermally conductive sheet disposed therebetween. The term “adhering” herein means that plural faces are in contact with each other owing to a chemical or physical force, or both.

The contact area in a semiconductor device assembled by adhering together a heat dissipating body and a plurality of heat generating bodies via a thermally conductive sheet is preferably 80% or more, more preferably 85% or more, further preferably 90% or more, and still more preferably 95% or more, with respect to the area of the face of each of the heat generating bodies or the heat dissipating body that faces the thermally conductive sheet.

For disposing the thermally conductive sheet between the heat generating body and the heat dissipating body, a method may be employed in which the thermally conductive sheet is first disposed on the heat generating body, after which the heat dissipating body is disposed thereon via the thermally conductive sheet, or a method may be employed in which the thermally conductive sheet is first disposed on the heat dissipating body, after which the plurality of heat generating bodies are disposed thereon via the thermally conductive sheet. Examples of such a method include a method in which a thermally conductive sheet is pasted to a heat dissipating body such as a heat spreader to be fixed temporarily, on which a plurality of heat generating bodies are disposed. According to this method, the process of temporarily fixing the thermally conductive sheet to each of the plurality of heat generating bodies can be omitted, whereby the thermally conductive sheet can be temporarily fixed easily. Further, this method tends to suppress occurrences of distortions or the like at the time of temporarily fixing the thermally conductive sheet.

From the viewpoint of simplifying the process, it is preferable that plural heat generating bodies are disposed on a single thermally conductive sheet. Further, a single heat dissipating body may be disposed on a single thermally conductive sheet, or plural heat dissipating bodies may be disposed on a single thermally conductive sheet.

The heat dissipating body and the plurality of heat generating bodies are adhered with each other via the thermally conductive sheet by applying pressure to the heat dissipating body and the plurality of heat generating bodies in a thickness direction of the thermally conductive sheet with the thermally conductive sheet disposed therebetween. In this process, the pressure may be applied from the side of the heat generating bodies, or from the side of the heat dissipating body.

The pressure applied in the thickness direction of the thermally conductive sheet is preferably from 0.05 to 10.00 MPa, more preferably from 0.10 to 5.00 MPa, and further preferably from 0.10 to 1.00 MPa, from the viewpoints of adhesion of the thermally conductive sheet and reducing the stress on the electronic component. The pressure is particularly preferably from 0.10 to 0.50 MPa from the viewpoint of reducing the stress on the electronic component.

The temperature during the application of the pressure is not particularly limited, and the temperature range is preferably determined in accordance with the type of the thermally conductive sheet. The temperature during the application of the pressure may be ambient temperature, and is preferably an increased temperature from the viewpoint of improving the compression ratio. The increased temperature may be, for example, from 80 to 200° C., from 100 to 190° C., or from 120 to 180° C.

It is particularly preferable that the pressure of from 0.10 to 1.00 MPa is applied in the temperature range of from 120 to 180° C. By the pressure being 0.10 MPa or more, or the increased temperature being 120° C. or more, favorable adhesion tends to be obtained. By the pressure being 1.00 MPa or less or the increased temperature being 180° C. or less, adhesion reliability tends to be further improved. It is thought that this is because thinning of the thermally conductive sheet caused by excessive compression can be suppressed, or because excessive increase in residual stress or deformation of surrounding members can be suppressed.

The amount of warpage of a heat generating body during the application of pressure, for example, the amount of warpage of a heat generating body when the pressure of 0.10 MPa is applied at 150° C., may be, for example, in at least one heat generating body, 10 μm or more, 20 μm or more, or 25 μm or more. The amount of warpage of a heat generating body during the application of pressure, for example, the amount of warpage of a heat generating body when the pressure of 0.10 MPa is applied at 150° C., may be, for example, in at least one heat generating body, 80 μm or less, 70 μm or less, or 60 μm or less. The above ranges may apply to the amount of warpage of a heat generating body under the pressure of 0.15 MPa at 150° C.

The amount of warpage of a heat generating body after the release of the pressure may be, for example, in at least one heat generating body, 40 μm or more, 50 μm or more, or 60 μm or more. The amount of warpage of a heat generating body after the release of the pressure may be, for example, in at least one heat generating body, 150 μm or less, 140 μm or less, or 130 μm or less. In a case in which the amount of warpage fluctuates in accordance with the temperature change after the release of the pressure, the “amount of warpage of a heat generating body after the release of the pressure” means the amount of warpage at 25° C.

In the process of adhering the heat dissipating body and the plurality of heat generating bodies, the difference between the amount of warpage of respective heat generating bodies during the application of the pressure and the amount of warpage of the same heat generating bodies after the release of the pressure may be, with regard to at least one heat generating body, 5 μm or more, 30 μm or more, 40 μm or more, or 50 μm or more. The upper limit of the difference with regard to at least one heat generating body may be, for example, 120 μm or less.

The “amount of warpage” of a heat generating body refers to the amount of maximum deformation (μm) in the thickness direction of the heat generating body during the deformation of the heat generating body by warpage.

An example of the method of measuring the amount of warpage will be explained with reference to FIG. 2 . Although a semiconductor device in the present disclosure has a plurality of heat generating bodies, FIG. 2 illustrates only one heat generating body for convenience. The amount of warpage can be measured based on the amount of deformation of the substrate mounted with a heat generating body as described below. The area subjected to the analysis of the amount of warpage is the area on which the heat generating body is mounted (the portion of the heat generating body “a”), viewed from the direction of the substrate. In the portion of the heat generating body “a”, the displacement between the portion having the maximum amount of deformation in the thickness direction of the substrate and the edge of the heat generating body is defined as the amount of warpage “b”.

The specific method for adhering the heat dissipating body and the plurality of heat generating bodies via the thermally conductive sheet is not particularly limited as long as it can fix the heat dissipating body and the plurality of heat generating bodies tightly adhered with each other. For example, a method may be employed in which a thermally conductive sheet is disposed between a heat dissipating body and a plurality of heat generating bodies and fixed with a jig capable of pressurizing them at approximately 0.05 to 1.00 MPa, in which state the plurality of heat generating bodies are allowed to generate heat, or is heated to 80 to 180° C. in an oven or the like. The examples also include a method in which a pressing machine capable of heating to 80 to 180° C. and applying pressure at 0.05 to 1.00 MPa is used.

The fixation may be performed by using a jig, such as a clip, a screw, or a spring. It is preferable that the heat generating bodies and the heat dissipating body are further fixed with a commonly employed means, such as an adhesive, from the viewpoint of maintaining adhesion.

The semiconductor device can be manufactured using a heat dissipating body and a plurality of heat generating bodies adhered with each other via a thermally conductive sheet, as described above. Examples of the semiconductor device include a semiconductor package having an integrated circuit, such as a GPU or a CPU, and a memory, such as an HBM, mounted on an interposer.

A specific example of the semiconductor device in one embodiment will be described in reference to FIG. 1 . Note that the embodiments are not limited thereto. Further, the sizes of the members in respective drawings are conceptual, and the relative relationships between the sizes of the members are not limited thereto.

A thermally conductive sheet 1 is used and tightly adhered to a plurality of heat generating bodies 2 on one side, while the other side is tightly adhered to a heat dissipating body 3. In FIG. 1 , the heat generating bodies 2 are fixed to a substrate 4 using an underfill material 5, and the heat dissipating body 3 is fixed to the substrate 4 using a seal material 5, the adherence between the thermally conductive sheet 1 and the heat dissipating body 3 and the heat generating bodies 2 being tightened by pressing them. By the heat dissipating body 3 and the plurality of heat generating bodies 2 being layered via the thermally conductive sheet 1, heat from the plurality of heat generating bodies 2 can be efficiently transferred to the heat dissipating body 3. If the heat is efficiently transferred, the life span of the semiconductor device for use is improved and a semiconductor device that stably functions for a long period of use can be provided. Further, even in a case in which the plurality of heat generating bodies 2 slightly differ in their height, in the process of adhering the heat dissipating body 3 and the plurality of heat generating bodies 2 via the thermally conductive sheet 1, the thermally conductive sheet can be compressed and adjust to the height difference by applying a pressure from the outside in the thickness direction, thereby favorably maintaining the adherence between the heat dissipating body 3 and the plurality of heat generating bodies 2. Further, adhering the plurality of heat generating bodies 2 to the heat dissipating body 3 using the thermally conductive sheet 1 can simplify the processes.

EXAMPLES

The invention will be described in detail below by way of Examples. However, the invention is not limited to these Examples. In the following Examples, the compression modulus, amount of compression, tack strength, thermal conductivity, amount of warpage, and contact area were evaluated by the following methods.

Measurement of Compression Modulus and Amount of Compression

A compression tester equipped with a thermostat chamber (INSTRON 5948 MICROTESTER, Instron Corporation) was used for the measurement. Thermally conductive sheets were cut into a circular shape of 14 mm in diameter for the test. The thermally conductive sheet was arranged between pieces of 0.1 mm-thick paper (release paper), to which a load was applied in the thickness direction of the thermally conductive sheet at a displacement rate of 0.1 mm/min in the thermostat chamber at a temperature of 150° C., during which the displacement (mm) and the load (N) were measured. The strain (dimensionless), which is determined as “displacement (mm)/thickness (mm)”, and the stress (MPa), which is determined as “load (N)/area (mm²)”, were plotted as the abscissa and the ordinate, respectively, and the slope at a stress of 0.10 MPa was defined as the compression modulus (MPa).

Measurement of Tack Strength

A universal physical property tester (TEXTURE ANALYZER, Eko Instruments Co., Ltd.) was used. A probe having a diameter of 7 mm was pressed against the thermally conductive sheet at a load of 40 N at 25° C. (ambient temperature), was maintained for 10 seconds, and thereafter was lifted. The tack strength (N·mm) was obtained as an area determined by integrating a load-displacement curve resulting therefrom.

Measurement of Thermal Conductivity

A thermally conductive sheet was cut into a 10 mm×10 mm piece, which was disposed between a transistor (2SC2233) and a copper block, which are a heat generating body and a heat dissipating body, respectively. A current was applied to the transistor while the transistor was pressed at a pressure of 0.14 MPa at 80° C., at which time the temperature of the transistor T1 (° C.) and the temperature of the copper block T2 (° C.) were measured. A thermal resistance value X per unit area of 1 cm² (K·cm²/W) was calculated based on the measured values and the applied electric power W1 (W) as follows.

X=(T1−T2)×1/W1

Further, the thermal conductivity λ (W/(mK)) was calculated using the thermal resistance (K·cm²/W) and the thickness t (μm) as follows.

λ=(t×10⁻⁶)/(X×10⁻⁴)

Measurement of Amount of Warpage

The amount of warpage was measured using a 3D thermal surface profiler (THERMOIRÉ PS200, Akrometrix, Inc.). The amount of warpage of the substrate corresponding to the chip area (20 mm×20 mm or 10 mm×10 mm) was measured.

The amount of warpage of the heat generating body during the application of a pressure of 0.15 MPa at 150° C. was 28 μm in the 20 mm×20 mm semiconductor chip, and 12 μm in the 10 mm×10 mm semiconductor chip. The amount of warpage of the heat generating body after the release of the pressure was 60 μm in the 20 mm×20 mm semiconductor chip, and 29 μm in the 10 mm×10 mm semiconductor chip.

Assessment Test of Contact Area

The contact area was assessed as follows. The state of adhesion was observed using an ultrasonic imaging diagnostic apparatus (INSIGHT 300, Insight Co., Ltd.) at 35 MHz by a reflection method. The obtained image was binarized using an image analysis software (ImageJ), and the ratio of the adhering area in the 20 mm×20 mm semiconductor chip portion or the 10 mm×10 mm semiconductor chip portion was calculated to obtain the contact area (%).

For the assessment of the contact area, simple packages fabricated as follows were used. MCL-E-700G(R) (0.81 mm in thickness, Hitachi Chemical Co., Ltd.) as a substrate, CEL-C-3730N-2 (Hitachi Chemical Co., Ltd.) as an underfill material, and a silicone-based adhesive (SE4450, Dow Corning Toray Co., Ltd.) as a seal material, were used. A 1 mm-thick copper plate having a nickel plating on the surface was used as a heat spreader. The substrate and the heat spreader had a size of 65 mm×65 mm. A semiconductor chip having a size of 20 mm×20 mm (height: 0.775 mm) and two semiconductor chips having a size of 10 mm×10 mm (height: 0.725 mm) were disposed on a substrate as illustrated in FIG. 3 . The spaces between the semiconductor chips were 5 mm.

The packages were assembled as follows. A thermally conductive sheet having a certain thickness was cut into a 23 mm×23 mm piece, which was pasted onto the heat spreader or the semiconductor chips. The substrate with the semiconductor chips and the seal material disposed thereon was covered by the heat spreader, which was then pressed in the thickness direction of the thermally conductive sheet using a high-precision pressure thermal bonding apparatus (HTB-MM, manufactured by Alpha-Design Co., Ltd.) under a certain pressure at a certain temperature. Subsequently, the members were placed in a thermostat chamber at 150° C. for two hours to completely cure the seal material.

Example 1

A 0.3 mm-thick thermally conductive sheet having a compression modulus of 1.16 MPa under a compressive stress of 0.10 MPa at 150° C., a tack strength of 7.6 N·mm at 25° C., and a thermal conductivity of 21 W/(mK), manufactured by Hitachi Chemical Co., Ltd., was selected, and was pasted to the heat spreader. The above-described substrate with three semiconductor chips and a seal material disposed thereon was covered by the heat spreader, with which a package was assembled in the above-described manner under the condition of 150° C., 0.15 MPa, thereby adhering the thermally conductive sheet to the semiconductor chips and the heat spreader, which are heat generating bodies and a heat dissipating body, respectively. The contact area at the 20 mm×20 mm semiconductor chip portion was 97%, and the contact areas at the two 10 mm×10 mm semiconductor chip portions were 99% and 99%, respectively. The contact area, which is an indicator of warpage adjustability, of 90% or more indicated a good warpage adjustability, and the plurality of heat generating bodies and the heat dissipating body were successfully adhered at once in a short time.

Example 2

A 0.2 mm-thick thermally conductive sheet having a compression modulus of 1.16 MPa under a compressive stress of 0.10 MPa at 150° C., a tack strength of 7.6 N·mm at 25° C., and a thermal conductivity of 18 W/(mK), manufactured by Hitachi Chemical Co., Ltd., was selected, and was pasted to the heat spreader. The above-described substrate with three semiconductor chips and a seal material disposed thereon was covered by the heat spreader, with which a package was assembled in the above-described manner under the condition of 150° C., 0.15 MPa, thereby adhering the thermally conductive sheet to the semiconductor chips and the heat spreader, which are heat generating bodies and a heat dissipating body, respectively. The contact area at the 20 mm×20 mm semiconductor chip portion was 95%, and the contact areas at the two 10 mm×10 mm semiconductor chip portions were 99% and 98%, respectively. The contact area, which is an indicator of warpage adjustability, of 90% or more indicated a good warpage adjustability, and the plurality of heat generating bodies and the heat dissipating body were successfully adhered at once in a short time.

Example 3

A 0.3 mm-thick thermally conductive sheet having a compression modulus of 1.16 MPa under a compressive stress of 0.10 MPa at 150° C., a tack strength of 7.6 N·mm at 25° C., and a thermal conductivity of 21 W/(mK), manufactured by Hitachi Chemical Co., Ltd., was selected. The thermally conductive sheet was first pasted to the three chips using the above-described substrate with plural semiconductor chips and a seal material disposed thereon, which was then covered by the heat spreader. A package was assembled in the above-described manner under the condition of 150° C., 0.15 MPa, thereby adhering the thermally conductive sheet to the semiconductor chips and the heat spreader, which are heat generating bodies and a heat dissipating body, respectively. The contact area at the 20 mm×20 mm semiconductor chip portion was 96%, and the contact areas at the two 10 mm×10 mm semiconductor chip portions were 98% and 97%, respectively. The contact area, which is an indicator of warpage adjustability, of 90% or more indicated a good warpage adjustability, and the plurality of heat generating bodies and a heat dissipating body were successfully adhered at once in a short time.

Example 4

A 0.15 mm-thick thermally conductive sheet having a compression modulus of 1.16 MPa under a compressive stress of 0.10 MPa at 150° C., a tack strength of 7.6 N·mm at 25° C., and a thermal conductivity of 16 W/(mK), manufactured by Hitachi Chemical Co., Ltd., was selected, and was pasted to the heat spreader. The above-described substrate with three semiconductor chips and a seal material disposed thereon was covered by the heat spreader, with which a package was assembled in the above-described manner under the condition of 150° C., 0.15 MPa, thereby adhering the thermally conductive sheet to the semiconductor chips and the heat spreader, which are heat generating bodies and a heat dissipating body, respectively. The contact area at the 20 mm×20 mm semiconductor chip portion was 92%, and the contact areas at the two 10 mm×10 mm semiconductor chip portions were 95% and 94%, respectively. The contact area, which is an indicator of warpage adjustability, of 90% or more indicated a good warpage adjustability, and the plurality of heat generating bodies and a heat dissipating body were successfully adhered at once in a short time.

Comparative Example 1

A liquid silicone grease (TK-P3K, manufactured by Sanwa Supply Inc.) having a thermal conductivity of 2 W/(mK) was selected as a thermally conductive material. Using the above-described substrate with three semiconductor chips and a seal material thereon, the grease was applied to the plural semiconductor chips, and the substrate was covered by the heat spreader, with which a package was assembled in the above-described manner under the condition of 150° C., 0.15 MPa, thereby adhering the grease to the semiconductor chips and the heat spreader, which are heat generating bodies and a heat dissipating body, respectively. The thickness of the silicone grease after the assembly was 40 μm. The contact area at the 20 mm×20 mm semiconductor chip portion was 84%, and the contact areas at the two 10 mm×10 mm semiconductor chip portions were 95% and 94%, respectively.

Comparative Example 2

A 0.3 mm-thick thermally conductive sheet having a compression modulus of 1.73 MPa under a compressive stress of 0.10 MPa at 150° C., a tack strength of 1.8 N·mm at 25° C., and a thermal conductivity of 23 W/(mK), manufactured by Hitachi Chemical Co., Ltd., was selected, and was pasted to the heat spreader. The above-described substrate with three semiconductor chips and a seal material disposed thereon was covered by the heat spreader, with which a package was assembled in the above-described manner under the condition of 150° C., 0.15 MPa, thereby adhering the thermally conductive sheet to the semiconductor chips and the heat spreader, which are heat generating bodies and a heat dissipating body, respectively. The contact area at the 20 mm×20 mm semiconductor chip portion was 78%, and the contact areas at the two 10 mm×10 mm semiconductor chip portions were 86% and 85%, respectively.

As described above, the methods employed in the Examples can easily adhere a plurality of heat generating bodies to a heat dissipating body at a time. Further, favorable contact area can be maintained, and therefore, it is thought that semiconductor devices having excellent heat dissipation can be obtained.

All the documents, patent applications and technical standards that are described in the present specification are hereby incorporated by reference to the same extent as if each individual document, patent application or technical standard is concretely and individually described to be incorporated by reference.

EXPLANATION OF REFERENCE NUMERALS

-   1 thermally conductive sheet -   2 heat generating body -   3 heat dissipating body -   4 substrate -   5 underfill material -   6 seal material -   10 semiconductor device -   a portion of heat generating body (area of analysis) -   b amount of warpage 

1. A thermally conductive sheet having a compression modulus of from 0.50 to 1.40 MPa under a compressive stress of 0.10 MPa at 150° C., the thermally conductive sheet being for use in adhering together a heat dissipating body and a plurality of heat generating bodies of a semiconductor device, by disposing the thermally conductive sheet between the heat dissipating body and the plurality of heat generating bodies.
 2. The thermally conductive sheet according to claim 1, wherein the thermally conductive sheet has a thermal conductivity of 7 W/(mK) or higher, the thermal conductivity being obtained using a thermal resistance measured by a steady state method. 